Yea any kind of messing with it besides rubbing off any LOOSE rust or powdery rust would affect value. A smooth brown gun is acceptable but back years ago people liked to try to sand them down to shiny original look which kills value for collectors now. Just protect what you got as it is. Well you could obtain replica rear sights and fix the lockwork. At least fixing the lockwork would not be visible on the outside and you could cock it. Probably needs a new sear, a nice replica or possibly original can be maybe had from Dixie Gun Works or someone like that. But then if you can cock it, someone might drop the hammer on the bare nipple and damage or flatten it out. They used to put a lead ball with a notch cut in to protect the nipple or you could just put something on the nipple to protect it from the hammer drop force but that is if you fix it. Original rear sights might be around for sale but they would be hit or miss onesies, no one probably has very many anywhere in one place anymore. And expensive.
Your gun is like your nose, it is just wrong for someone else to pick it for you!